Purification of titanium compounds



Patented May 26, 1936 UNITED STATES PATENT OFFICE PURIFICATION orTITANIUM COMPOUNDS Svend' S. Svemlsen, Madison, Wis.,' assignor toBurgess Titanium Company, Madison, Wis., a corporation of Delaware NoDrawing. Application June 4, 1935,

Serial No. 24,820

'1 Claims. (01. 23-88) This application is a continuation in part of mycopending application Serial No. 745,753. filed September 27,1934.

It is an object of this invention to provide a method for purifyingtitanium compounds and especially a method whereby the iron contentthereof may be decreased to a negligible amount.

I have found that when titanium-bearing ores,

especially the oxide ores such as ilmenite and rutile, are treated, asdescribed in the above application, with reactive fluorides, such asammonium fluoride or ammonium bifluoride,

whereby a water soluble titanium'fluoride or fluoride compound isformed, the small amounts of heavy metals, particularly iron, remainingsoluble in water solution thereof may be separated from the titanium ifsuch solution is treated as described herein. These metals, andespecially iron, must be removed from the titanium salts if a high gradeof white titanium oxide pigment is to be made therefrom. The iron ispresent in as preciable amount with the iron sulfide. I have foundfurther that this effect of the fluoride salts in effecting a separationof the-iron from the titanium is heightened by the presence of anadditional soluble fluoride salt such as ammonium 40 fluoride.

In order to remove iron as an insoluble sulfide from solutionscontaining its salts, such solutions I must not be acidic. Solutions ofthe ordinary titanium salts, such as the'sulfate, which is used ,45extensively in the production of titanium oxide pigment, hydrolyze whenneutral and especially-if a soluble sulfide is added to the solution. Ittherefore is impossible or impracticable to remove iron byprecipitatingit 'as the sulfide from such 50 solutions. I have discovered, however,that it is possible to regulate solutions of titanium fluoride saltswithin narrow limits of hydrogen ion concentration, whereby when asoluble sulfide is added, the iron is precipitated substantially quan-55 titatively therefrom without simultaneously predigestion continuinguntil the temperature lo such solutions as iron fluoride. If ammoniumcipitating appreciable amounts of titanium. I

have further found that the tendency of the soluble sulfide to formtitanium hydrate or other insoluble titanium compound in. such titaniumfluoride solutions seems to be depressed further 5 by the presence of anadditional soluble fluoride salt, such as ammonium fluoride. It isdesirable therefore to have such a salt-present in a solution which isto be treated with a soluble sulfide.

Titanium fluoride compound solutions may be. 10

made conveniently as described in the above referred to application bydigesting flnely ground ilmenite with a concentrated solution ofammonium fluoride or bifluoride-in large excess, the

reaches a temperature of 150-180 C. or until most of the water is drivenfrom' the reaction mass. The large excess (usually 50% or more than thestoichiometric amount) of the ammonium fluoride which is used to securecom- 20 plete conversion of theilmenite into fluorides, also has theadvantage oi adding the desired excess of ammonimn fluoride to theresulting titanium fluorides. The titanium fluorides so producedapparently are tetrafluorides and this invention is directedparticularly to the use of such tetrafluorides. The residue, a grayishpaste or powder, is lixiviated with'water and filtered, the

iron and ammonium double fluoride being practically insoluble. '1hefiltrate is a solution of ammonium fluoride and titanium fluoridecompound containing small amounts of dissolved iron fluoride as animpurity.

The solution so formed is acidic and must be neutralized, preferablywith ammonia, to the point at which the addition of more ammoniaprecipitates out permanently titanium hydrate or .acrystalline titaniumcompound. This point is designated as substantially neutral" forconvenience hereinafter, usually at a pH of about 8.8, 40

and must be closely maintained until the insoluble sulfldesare removedfrom this solution.

After this condition is attained, a convenient soluble sulfide is addedto the solution to precipk tate iron and other heavy metals. Ammoniumsulfide may be used. Sodium or potassium sul-, fldes or hydrogen sulfideare other soluble sulfides that may be used. If hydrogen sulflde isused, additional alkali is required to maintain the necessary neutralityor theiron sulfide will be dissolved. 'Ihe'iron and other heaw metalsdissolved in the titanium fluoride solution are precipitated as sulfideseither in a hot or cold solution, a hot solution (about 50-60 C.) beingpreferred. The precipitate may be filtered readily from the solutiontogether with any other insolubles that may be present. The iron sulfideis precipitated as the ferrous salt, the ammonium sulfide reducing anyferric salts to the ferrous condition. Precautions must be taken topreventthe ferrous sulfidefrom being again oxidized to the ferriccondition whereby it will again dissolve in the fluoride solution beforeit is separated from the solution.

In general the ratio of NH4F toTiFi in solution should be greater than 1to 1 by weight and less than 5 to 1 by weight, thoughthe invention isnot limited to proportions within these limits. A convenientconcentration is one in which the specific gravity is about 1.110 to1.125 (at 60 C.)

.. When a titanium tetrafiuoride is referred to in the claims, thiscovers titanium tetrafiuoride as such and also associated or combinedwith other salts as double salts or compounds, ammonium fiuotitanatebeing an example of such a compound.

Although in the above disclosure the titanium fluoride solution isneutralized before adding the i soluble sulfide, it will be obvious tothose skilled in the art that the soluble sulfide, especially hydrogensulfide, may be added to the solution before neutralizing. Uponneutralizing the thus sulfide-containing solution the iron sulfide isprecipitated. This variation is within the scope of the appended claims.

I claim:

1. In the treatment and purification of titan ium compounds, adding asoluble sulfide to a substantially neutral solution of a titaniumtetrafluoride, and maintaining the neutrality of said solution toprecipitate dissolved heavy metals therefrom.

2. In the treatment and purification oi titanium compounds, addingammonium sulfide to a substantially neutral solution of a titaniumtetrafiuoride. and maintaining the neutrality of said solution toprecipitate heavy metals therefrom.

3. In the treatment and purification of titanium compounds, adding asoluble sulfide to a substantially neutral. solution of a titaniumtetrafiuoride containing ammonium fluoride. and

' maintaining the neutrality of said solution to precipitate dissolvedheavy metals therefrom.

4. In the treatment and purification of titanium compounds, addingammonium sulfide to a substantially neutral solution of a titaniumtetrafiuoride containing ammonium fluoride, and

maintaining the neutrality of said solution to precipitate dissolvediron therefrom.

5. In the treatment and purification of titanium compounds, adding asoluble sulfide to a substantially neutral solution of a titaniumtetrafiuoride containing ammonium fluoride wherein the ratio of .NH4F toTim is from 1:1 to 5:1,- and maintaining the neutrality of said solutionto precipitate dissolved heavy metals therefrom.

6. In the treatment and purification of titanium compounds, addingammonium sulfide to a substantially neutral solution of a-titaniumtetrafiuoride containing ammonium fiuoride wherein the ratio of NHQF toTiF4 is from 1:1 to 5:1, and maintaining the neutrality of said solutionto precipitate dissolved iron therefrom.

'7. In the treatment and purification of titanium compounds, addingammonium sulfide to a substantially neutral solution of a titaniumtetrafiuoride containing ammonium fiuoride, maintaining the neutralityof said solution and removing the insolubles therefrom while maintainingreducing conditions therein.

SVEND S. SVENDSEN.

